Catalytic method and apparatus for separating a gaseous component from an incoming gas stream

ABSTRACT

A process for separating at least a portion of an acid gas from a gaseous mixture, said process comprising contacting the gaseous mixture with an absorption medium and/or adsorption medium, wherein said medium absorbs and/or adsorbs at least a portion of the acid gas to form a rich medium; and separating at least a portion of the acid gas from the rich medium to form a lean medium; wherein the separation step is performed in the presence of an acid catalyst.

FIELD

This disclosure relates to the use of a catalyst in the separation of acomponent or components from a gas stream. In one aspect amulti-component gas stream comprising an acid gas (e.g. carbon dioxide(CO₂), hydrogen sulfide (H₂S), etc.) is at least partially purified ofsaid acid gas.

BACKGROUND

A wide variety of technologies exist for removing a component orcomponents from a mixture that also includes other components. Theseinclude distillation, gas absorption, rectification, stripping,regeneration, solvent extraction, etc. In each case, the traditionaltechnology involves the use of vessels, example columns, to effectseparation. Specifically, in the cases of distillation, gas absorption,stripping, rectification, regeneration, etc., the columns contain columninternals such as packing or trays which are devices to provide thesurface area for contact between two phases to cause the separation ofcomponents. This physical contact area separates the liquid flow intodroplets which allows the gas to have a bigger area of intimate contactwith the liquid. The performance of the device used to provide suchsurface area of contact is evaluated on such physical basis as thesurface area per unit volume, wettability, pressure across the vessel,etc.

It has been suggested that, in the case of distillation, a chemicalcontribution (e.g. a catalyst) may be used in addition to the physicalcontribution. However, this strategy has not been applied in the removalof a component or components from a multi-component gas stream. Examplesof such multi-component gas streams are combustion flue gases, naturalgases, reformate gases, refinery gas, off gases from cementmanufacturing, steel making, and the like. In these examples, thecomponents that can be removed include, for example, CO₂, SO₂, SO₃, H₂S,and/or NH₃.

In the case of combustion flue gases, refinery off gas, and reformategas, it is known that the production and use of fossil fuels contributeto an increase in emissions of greenhouse gases (GHGs), especiallycarbon dioxide (CO₂) and other pollutants such as oxides of sulfur(SO_(x)), oxides of nitrogen (NO_(x)), hydrogen sulphide (H₂S) andhydrogen chloride (HCl). It is desirable to reduce the emissions of CO₂or the other pollutants. Large sources of CO₂ emissions such ascoal-fired power plants, refineries, cement manufacturing and the likeare targeted to achieve these reductions. Thus, intensive researchefforts have been made in recent years to develop methods for recoveringthe CO₂ emitted from gas streams from these huge industrial emitters,and for storing the recovered CO₂ without discharging it into theatmosphere.

One method of CO₂ capture is gas absorption using aqueous aminesolutions or ammonia solutions. Typically this method of gas separationtechnology is used to absorb CO₂ from low-pressure streams such as fluegases emitted from power plants. An example of an amine used in thistype of process is monoethanolamine (MEA). From a molecular structuralstandpoint, one of the advantages of using amines is that they containat least one hydroxyl group, which helps to reduce vapor pressure andthus minimize the losses of the product during hot amine regeneration orCO₂ stripping from the amine. Another advantage of using amines is thatthe presence of the hydroxyl group increases the solubility of theamines in aqueous solutions, thus allowing the use of highlyconcentrated absorbing solutions. Yet another advantage of using aminesis that the presence of the amino group provides the necessaryalkalinity to absorb CO₂ (Kohl, A. L. and Reisenfeld, F. C., GasPurification, 4^(th) ed., Gulf Publishing Co., Houston, Tex., 1985;Kohl, A. L. and Nielsen, R. B., Gas Purification, 5^(th) ed., GulfPublishing Co., Houston, Tex., 1997). Thus, amines and ammonia have beenthe solvent of choice for CO₂ removal on a commercial scale. Inparticular, aqueous amine solutions are the widely used solvents for CO₂and H₂S absorption.

For many years, the amine process or the ammonia process for CO₂ captureremained unchanged but recently demands to reduce energy consumption,decrease solvent losses, and improve air and water qualities haveresulted in several modifications being introduced. For example, in thecase of the amine process, specially formulated solvents have beenintroduced. Depending on the process requirements, for example,selective removal of H₂S and/or CO₂-bulk removal, several options foramine-based treating solvents with varying compositions are available.Also, improvements involving the overall integration and optimization ofthe plant configuration have been suggested. For example, U.S. Pat. No.6,800,120 (Won et al.) describes a process configuration has beendeveloped that allows the reduction of the heat duty for regeneration.Other improvements on CO₂ capture technologies have been highlighted(Yagi et al., Mitsubishi Heavy Industries, GHGT7, Vancouver, 2004) basedon solvent improvement, and special design of certain process units. CA2,685,923 (Gelowitz et al.) describes a number of process configurationsas well as a different amine formulation, the combination of which issaid to achieve reductions in the heat duty for regeneration.

In a typical system, CO₂ capture by absorption using chemical liquidabsorbent involves absorbing CO₂ from the flue gas stream into theabsorbent flowing down from the top of the absorber columncounter-currently with the flue gas stream, which flows upwards from thebottom of the column. The CO₂ rich liquid from the absorber column isthen pumped through the lean/rich exchanger to the top of the strippercolumn where CO₂ is stripped off the liquid by application of steamthrough a reboiler thereby regenerating the liquid absorbent. Thechemical absorption of CO₂ into the liquid absorbent in the absorber isexothermic. The stripping of CO₂ from the liquid absorbent in thestripper is endothermic and requires external heating. Typically thelowest temperature in the absorber column is around 60° C., which islimited by the temperatures of the lean liquid absorbent and flue gasstream temperatures, and the highest temperature is around 90° C. Thetypical temperature for stripping or desorption is in the range of 105°C.-150° C. The CO₂ desorption process is endothermic with a much higherheat demand than the absorption process can provide thus setting up atemperature mismatch between the absorber and regenerator/stripper. Thisis one of the reasons that a large amount of external energy is requiredto induce CO₂ stripping in the desorption tower. Since CO₂ stripping ispart of the CO₂ capture process that employs chemical absorption,minimizing this external heat supply would be advantageous.

There has been interest in estimating the heat of chemical absorption ofCO₂ into liquid absorbents and the heat duty for stripping CO₂ from theliquid absorbents for absorbent regeneration. Mechanistic verificationwould allow modifications to be designed aimed lowering the energyrequired for activation (e.g. Silva, E. F., Svendsen, H. F., 2006. Studyof the Carbamate Stability of Amines using ab initio Methods and FreeEnergy Perturbations. Ind. Eng. Chem. Res. 45, 2497; Silva, E. F.,Svendsen, H. F., 2007. Computational chemistry studies of reactionsequilibrium of kinetics of CO₂ absorption. International Journal ofGreenhouse Gas Control I, 151; Jamal, A., Meisen, A., Lim, C. J., 2006.Kinetics of carbon dioxide absorption and desorption in aqueousalkanolamine solutions using a novel hemispherical contactor-I:Experimental apparatus and mathematical modeling. Chemical EngineeringScience 61, 6571; Jamal, A., Meisen, A., Lim, C. J., 2006. Kinetics ofcarbon dioxide absorption and desorption in aqueous alkanolaminesolutions using a novel hemispherical contactor-II: Experimental resultsand parameter estimation. Chemical Engineering Science 61, 6590).However, there has been limited study of the detailed analysis of thereaction pathway at an atomic level. The structure optimization, energydiagram, and transition-state exploration of the absorption anddesorption processes are not clearly understood.

SUMMARY

In this disclosure, we use a combination of computational chemistrymethods and experimental thermodynamic analysis to investigate thereaction enthalpy of CO₂ absorption for amine-H₂O—CO₂ systems. We haveused this knowledge to generate an accurate free energy diagram of thezwitterion mechanism for CO₂ desorption with transition-stateexploration, intermediate species structure optimization and analysis.This disclosure provides processes, methods, compositions, devices, andapparatus for the capture of acid gases, such as carbon dioxide (CO₂),from flue gas streams, reformate gas streams, natural gas streams, orother industrial gas streams.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Simulation of CO₂ desorption in the MEA-CO₂—H₂O system in theGaseous Phase using HF/6-31G(d) [1: carbamate, H⁺, H₂O; 2: zwitterions,H₂O; 3: N—C stretching in zwitterions, H₂O; 4: CO₂ dissociates from MEA,H₂O];

FIG. 2: Detailed linear (left hand side) and circular (right hand side)structures of the reactants (MEA-CO₂), reaction intermediate(zwitterion), and products (MEA+CO₂) for CO₂ desorption;

FIG. 3a : Relative (kcal mol⁻¹) Energy Diagram of the ZwitterionMechanism Showing Two Possible Structures;

FIG. 3b : Detailed reaction pathway of the Zwitterion mechanism fromreactants through intermediates to products corresponding to the energydiagram of FIG. 3a for the linear case;

FIG. 4: Overall CO₂ desorption mechanism with Solid Acid (e.g. Al)catalyst;

FIG. 5: The reaction pathway for desorption of CO₂ (carbamate breaking)over a solid acid catalyst-comparison of energy between catalytic andnon-catalytic approaches;

FIG. 6: Experimental apparatus for Batch CO₂ desorption from CO₂ LoadedAmine Solution;

FIG. 7: Experimental Setup to Test the Effect of Solid AlkalineCatalysts for CO₂ Absorption;

FIG. 8: Process configuration Used to Test Catalytic CO₂ Absorption andDesorption;

FIG. 9: Desorbed CO₂ Flow Rate as a Function of Desorption Temperaturefor Different Amounts of Solid Acid HZSM-5 Catalyst;

FIG. 10: Desorbed CO₂ Flow Rate (L/min) for 300 ml of Rich MEA Solutionwith 65.0 g H-ZSM-5 for Various Molarities and Loading;

FIG. 11: Catalysis of CO₂ desorption of 5M MEA solution under 65.0 gHZSM-5 Catalyst with different MEA loadings;

FIG. 12: Desorbed CO₂ Flow Rate (L/min) for 300 ml of Rich MEA Solution(5M, α=0.45) for Different Types of Solid Acid Catalysts (HZSM-5=H-1 andγ-Al₂O₃=A-2);

FIG. 13: CO₂ absorption rate for Various Amounts of MgCO₃ Catalyst.

DETAILED DESCRIPTION

The present disclosure relates to processes, methods, compositions,devices, and apparatus for the separation of a component or componentsfrom a gas stream. The present processes, methods, compositions,devices, and apparatus may provide, for example, improved absorbercapture efficiency, increased gas production rate, reduced energyconsumption, lower capital costs, and/or lower operating costs. Thepresent processes, methods, compositions, devices, and apparatus arebased on the use of catalysts in the absorber and/or the stripper.

Particularly, the present disclosure provides a method for using analkaline catalyst in the absorber to facilitate acid gas absorption inan absorbent, and/or an acid catalyst in the stripper column tofacilitate stripping of the acid gas.

The present disclosure provides a method for employing a solid alkalinecatalyst in the absorber to facilitate acid gas absorption by the liquidabsorbent, and/or a solid acid catalyst in the stripper column tocatalyze stripping.

The present disclosure provides a catalyst, catalytic device, catalyticpacking material, catalytic column internals, or the like for separationof a component or components from a mixture of components. Theseparation may be achieved by any suitable method such as, for example,distillation, absorption, stripping, rectification, desorption, and thelike.

The present catalytic process may be used, for example, for removal of agas component or components (e.g. carbon dioxide (CO₂), hydrogen sulfide(H₂S), etc.) from multi-component gas streams (e.g. combustion flue gas,reformate gas and natural gas). While not wishing to be bound by theory,it is believed that the presence of the catalyst shifts the separationmechanisms or pathways for the various processes in favor of loweractivation energy for separation thereby improving the efficiency of theprocess. Particularly, the present disclosure provides a method forusing an alkaline catalyst in the absorber to facilitate acid gasabsorption in the liquid absorbent, and/or an acid catalyst in thestripper column to facilitate CO₂ stripping from the liquid absorbent.

The method may lead to cost and process improvements. For example, theexternal heat requirements for removing an acid gas from a gas stream byan amine-containing liquid absorbent or an ammonia solution may bereduced.

The present disclosure further relates to the development of acatalytically reactive packing material or column internals forseparation by catalytic distillation, and/or absorption, and/orstripping, and/or desorption, and/or rectification, and/or removal of agas component or components from a multi-component gas stream.

As used herein, the term ‘absorption media’ and ‘adsorption media’refers to media that can absorb/adsorb an amount of acid gas.

As used herein, the term ‘rich absorption and/or adsorption media’refers to media that has absorbed/adsorbed an amount of acid gasrelative to lean media.

As used herein, the term ‘lean absorption and/or adsorption media’refers to media that has no or low amounts of acid gas.

Absorption/adsorption media that may be used herein includemonoethanolamine (MEA), diglycolamine (DGA), diethanolamine (DEA),methyldiethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP),piperazine (PZ), ammonia, amines, alkanolamines, amino alcohols,diamines, ionic liquids, aminosilicone, derivatives and/or combinationsthereof.

As used herein, the term ‘acid gas’ refers to gases that form acidicsolutions when mixed with water. Examples of acid gases include carbondioxide (CO₂), sulphur dioxide (SO₂), sulphur trioxide (SO₃), hydrogensulphide (H₂S), hydrogen chloride (HCl), and oxides of nitrogen(NO_(x)).

As used herein, the term ‘acid catalyst’ refers to proton donor(Brønsted acid) catalysts, electron acceptor (Lewis acid) catalysts, andcombinations thereof. Any suitable acid catalyst may be used herein. Forexample, the catalyst may be a proton-donating catalyst, or anelectron-acceptor catalyst. Preferred catalysts are proton-donators.Examples of acid catalysts include, but are not limited to, FeCl₃, SbF₅and AlCl₃ supported on graphite, Al₂O₃, SiO₂, zeolites, & clays (e.g.AlCl₃/Al₂O₃, ZnCl₂/Acid treated clays, FeCl₃/graphite, SbF₅/graphite,AlCl₃/graphite, vanadium phosphates and aluminophosphates, CaO—ZrO₂;Sm₂O₃—ZrO₂; Yb₂O₃—ZrO₂, aluminum chlorofluoride, ACF, (AlCl_(x)F_(3-x),x≈0.05-0.25), aluminum bromofluoride, ABF, (AlBr_(x)F_(3-x),x≈0.05-0.25)); heteropoly acids (HPAs) such as H₃PW₁₂O₄₀ and H₃PMo₁₂O₄₀;silica-supported Nafion (SAC-13); alumina, amorphous silica-alumina,amorphous silica-alumina molecular sieves such as microporousaluminosilicates or zeolites (e.g. HZSM-5, H—Y, H—X) and mesoporousaluminosilicates such as M41S (e.g. MCM-41, SBA-15, MCF);silica-magnesia, silica-zirconia, alumina-boria, titania-boria,tungstate-alumina, and tungstate zirconia; AlCl₃/mesoporous silica,CrO_(x)/ZrO₂, sulfated zirconia, pillared clays (PILC) and acidic porousclay heterostructures (PCH).

Any suitable Brønsted acid catalyst may be used herein. For example,amorphous silica-alumina molecular sieves such as microporousaluminosilicates or zeolites (e.g. HZSM-5, H—Y, H—X) and mesoporousaluminosilicates such as M41S (e.g. MCM-41, SBA-15, MCF); heteropolyacids (HPAs) such as H₃PW₁₂O₄₀ and H₃PMo₁₂O₄₀; silica-supported Nafion(SAC-13), and combinations thereof.

Any suitable Lewis acid catalyst may be used herein. For example, FeCl₃,SbF₃ and AlCl₃ supported on graphite, Al₂O₃, SiO₂, zeolites, & clays(e.g. AlCl₃/Al₂O₃, ZnCl₂/Acid treated clays, FeCl₃/graphite,SbF₅/graphite, AlCl₃/graphite, vanadium phosphates andaluminophosphates, CaO—ZrO₂; Sm₂O₃—ZrO₂; Yb₂O₃—ZrO₂, aluminumchlorofluoride, ACF, (AlCl_(x)F_(3-x), x≈0.05-0.25), aluminumbromofluoride, ABF, (AlBr_(x)F_(3-x), x≈0.05-0.25), and combinationsthereof.

Any suitable mix of Brønsted acid catalyst and Lewis acid catalyst maybe used herein. For example, alumina, amorphous silica-alumina,amorphous silica-alumina molecular sieves, silica-magnesia,silica-zirconia, alumina-boria, titania-boria, tungstate-alumina, andtungstate zirconia; AlCl₃/mesoporous silica, CrO_(x)/ZrO₂, sulfatedzirconia, pillared clays (PILC) and acidic porous clay heterostructures(PCH).

As used herein, the term ‘alkaline catalyst’ refers to proton acceptorcatalysts, electron donor catalysts, and combinations thereof. Anysuitable alkaline catalyst may be used herein. For example,electron-donating (Lewis base) catalysts may be used. Examples, ofalkaline catalysts include, but are not limited to, Na/NaOH/Al₂O₃,Quaternary ammonium functionality supported over a resin (A26),Quaternary ammonium salt functionalized silica gel (QN⁺OH⁻/SiO₂), ZnO,ZrO₂, ThO₂, TiO₂, CaO, MgO, SrO, BaO; Na metal dispersed on Al₂O₃,Na/MgO, La₂O₃, Y₂O₃, alkali metal oxides, alkali metal ions on alumina(K⁺/Al₂O₃; Na⁺/Al₂O₃), alkali metal ions on silica (K⁺/SiO₂; Na⁺/SiO₂),alkali metal on alkaline earth oxide (Na/MgO), alkali metals and alkalimetal hydroxides on alumina (Na/NaOH/Al₂O₃), clay minerals (such ashydrotalcite, chrysotile, sepiolite), non-oxide, KF supported onalumina, lanthanide imide and nitride on zeolite, and combinationsthereof.

Any suitable electron-donating catalyst may be used herein. For example,Na metal dispersed on Al₂O₃, Na/MgO, and combinations thereof.

The present technology may be used in a variety of situations. Forexample, in the treatment of exhaust gases from electric powergenerating plants; exhaust and off gases from breweries and ethanolplants; exhaust and off gases from cement manufacturing plants; refineryoff gases; reformate gas or product gas mixture from reforming plants toproduce hydrogen; biogas; combustion flue gas to produce steam for steamassisted gravity drainage (SAGD) operations for crude oil and oil sandsproduction; natural gas processing.

The present catalyst may be presented in any suitable form. For example,in the form of (a) pellets (cylinders, spheres, random shapes, etc.) inthe stripper or absorber, (b) sprayed on typical absorber or stripperinternals (structured packing, random packing, trays, etc.), (c) coatedon typical absorber or stripper internals (structured packing, randompacking, trays, etc.), (d) in a honey-comb style in the absorber orstripper, (e) in the form of pellets (cylinders, spheres, random shapes,etc.) or sprayed or coated on the inside of pipes or on pipe internals(packing) or in a honey-comb style in the pipe carrying the loaded aminefrom the lean-rich exchanger or cross flow heat exchanger (but after theheat exchanger) to the stripper, (f) in the same manner as in (e) of anypipe carrying heated or hot rich amine, (g) in the form of pellets(cylinders, spheres, random shapes, etc.) on the amine side of thereboiler or sprayed or coated on tubes on the amine side of thereboiler.

The present disclosure provides a process for separating at least aportion of an acid gas (e.g. CO₂) from a gaseous mixture, said processcomprising:

(a) contacting the gaseous mixture with an absorption medium and/oradsorption medium, wherein said medium absorbs and/or adsorbs at least aportion of the acid gas to form a rich medium; and

(b) separating at least a portion of the acid gas from the rich mediumto form a lean medium; wherein the separation step is performed using anacid catalyst, a proton-donating catalyst, an electron withdrawingcatalyst, or a combination thereof.

The present disclosure provides a process for separating at least aportion of an acid gas (e.g. CO₂) from a gaseous mixture, said processcomprising:

(a) contacting the gaseous mixture with an absorption medium and/oradsorption medium, wherein said medium absorbs and/or adsorbs at least aportion of the acid gas to form a rich medium; and

(b) separating at least a portion of the acid gas from the rich mediumto form a lean medium; wherein the absorption/adsorption is performedusing an alkaline catalyst, an electron donating catalyst, or acombination thereof.

The present disclosure provides a process for separating at least aportion of an acid gas (e.g. CO₂) from a gaseous mixture, said processcomprising:

(a) contacting the gaseous mixture with an absorption medium and/oradsorption medium, wherein said medium absorbs and/or adsorbs at least aportion of the acid gas to form a rich medium; and

(b) separating at least a portion of the acid gas from the rich mediumto form a lean medium; wherein the absorption/adsorption is performedusing an alkaline catalyst, an electron donating catalyst, or acombination thereof; and the separation is performed using an acidcatalyst, a proton-donating catalyst, an electron withdrawing catalyst,or a combination thereof.

Post combustion capture of CO₂ from flue gases using amines wasexamined. The requirement for a large external heat supply duringamine-based post combustion capture in order to strip CO₂ from loadedamine and the need for a taller column for CO₂ absorption can beillustrated in an energy diagram constructed to show CO₂ absorption in alean amine and CO₂ stripping from CO₂ loaded amine solution. Thepostulated mechanism of CO₂ absorption and desorption is based on theso-called “Zwitterion mechanism” proposed by Caplow in 1968. This isconsidered to be a two-step mechanism (Equations 1 and 2) for bothabsorption and desorption. These steps are two reversible reactions andone short-lived intermediate. In the absorption process or “carbamateformation” (i.e. from left to right), the steps are a zwitterionformation and a deprotonation. In the desorption process or “carbamatebreakdown” (i.e. from right to left), the steps are a proton-transferprocess and a N—C bond breaking process. These two reactions can beexpressed in reactions (1) and (2).MEA+CO₂+H₂O←→MEA-H⁺—CO₂ ⁻+H₂O  (1)MEA-H⁺—CO₂ ⁻+H₂O←→MEA-CO₂ ⁻+H₃O⁺  (2)

It has been suggested (Crooks, J. E., Donnellan, J. P., 1989. Kineticsand Mechanism of Reaction Between Carbon Dioxide and Amine in AqueousSolution. J. Chem. Soc. Perkins. Trans., II, 331) a one-step mechanismof carbamate formation (Equation 3). It should be noted that forabsorption, the one-step and two-step mechanism of CO₂ absorption arenot contradictory. Based on the zwitterion mechanism, the first slowstep of the zwitterion formation is the rate determining step whichfacilitates the subsequent deprotonation step. The second step thusoccurs automatically and rapidly such that the total absorption processcan be regarded as one-step.(General): R₂NH+CO₂+B←→R₂N—CO₂ ⁻+HB⁺(MEA): MEA+CO₂+MEA-CO₂+H₂O←→MEA-CO₂ ⁻+H₃ ⁺O  (3)

In contrast, the Zwitterion mechanism of CO₂ desorption would need to bea two-step mechanism. The present disclosure reproduces the desorptionprocess in the gaseous phase using the Hartree-Fock theory (HF/6-31 G(d)method) optimizing for the reaction between carbamate and H₃O⁺. As usedin this context, optimization means molecular structural geometryoptimization designed to locate the energy minima on a potential energysurface for the purpose of predicting the equilibrium structures ofmolecular systems. Since cations and anions have very high energy in thegaseous phase, there is no transition state during the desorptionprocess and the reaction occurs automatically. FIG. 1 represents theintermediate converging process in the gas phase. It represents CO₂desorption in the gas phase using the zwitterion mechanism i.e. via atwo-step pathway from (i) proton transfer to N—C bond breaking.

The structure of MEA+CO₂, Zwitterions and carbamate was optimized basedon the Zwitterion mechanism, as shown in FIG. 2. This detailed structureanalysis was used to evaluate the applicability of the mechanism. On thebasis of this optimization analysis, it was found that the molecularorbital hybridization of the nitrogen atom in the three species wasquite different; the N atom is sp³ hybridized in MEA and Zwitterions,but is sp² hybridized in the carbamate. This suggests a change inmolecular structure when a carbamate evolves into a zwitterion. Adetailed comparison of the structures in terms of N—C and C—O bondlengths was performed (Table 3).

TABLE 3 Linear and Circular Structures of the Reactant, Product andReaction Intermediates for the Zwitterion Linear structure^(b) (Å)Circular structure (Å) Bond Length R_(N—C) R_(C—O) R_(C—O) R_(N—C)R_(C—O) R_(C—O) MEA + CO₂ — 1.143 1.143 — 1.143 1.143 Transition State1.926 1.173 1.173 1.930 1.173 1.173 Zwitterion 1.553 1.208 1.211 1.5541.206 1.212 (sp³) Zwitterion 1.450 1.227 1.230 1.438 1.226 1.239 (sp²)MEA-CO2− 1.395 1.242 1.245 1.388 1.240 1.251 MEA-COOH 1.337 1.208 1.3261.332 1.213 1.321 ^(a)All the structures were optimized with HF/6-31G(d)with CPCM solvent shell except that Zwitterion (sp²) is the startinggeometry. ^(b)The detailed structures are illustrated in FIG. 2.

In the optimized structures of MEA and CO₂, the normal N—C bond lengthin MEA was 1.45 Å with nitrogen being sp³ hybridized, while the C—O bondlength was 1.14 Å and was sp hybridized. The N—C bond in MEA is a singlebond, while the C—O bond is between a double bond and a triple bond. Inthe optimized structure of a carbamate, the N—C bond in contact with CO₂was shortened to 1.395 Å while the C—O bond was stretched to 1.24 Å;both bonds are approximate to double bonds. The averaged bond lengthsare due to the de-localized conjugation. The N atom of the carbamate issp² hybridized; N, C with two O atoms that are almost arranged inone-plane. The lone pair 2p orbital of nitrogen conjugates with the 2porbital of C and O atoms. Four 2p orbitals stand perpendicular to theplain, and then generate a huge de-localized π bond over N, C and two Oatoms. This conjugation structure stabilizes the carbamate and improvesthe absorption ability of MEA.

The optimized structure of the Zwitterion is quite different from thatof the carbamate. In the optimized structure of the zwitterion, the Natom is sp³ hybridized, with the N—C bond stretched to 1.55 Å and C—Obond shortened to 1.21 Å which indicates that the conjugation is brokenand the structure is closer to MEA+CO₂ than the carbamate. The protontransfer breaks the conjugation of the carbamate not only by switchingfrom sp² to sp^(a) formation, but also, by lengthening the N—C bond toweaken the bong strength. Thus the proton greatly facilitates CO₂stripping by promoting the second CO₂ desorption step (i.e. N—C bondbreaking). Therefore proton transfer appears to be indispensable for CO₂desorption (carbamate breakdown).

The energy associated with proton transfer was estimated in order toestimate the contribution of the proton for stripping. Since theZwitterion is a short-live intermediate, it is challenging to estimatethe enthalpy experimentally hence computational methods were applied.Reaction (2) has a charge separation issue. Also, the computed energy ofcarbamate+H₃O⁺ is even higher than the Zwitterion, which wouldcontradict experimental observations. Thus, this cannot be calculateddirectly.

In order to estimate the energy required for the proton transfer that isnecessary for stripping, a short-live intermediate MEACOOH (carboxylacid) was induced to create a reaction circle as presented in reactions(4) and (5). The energy of reaction (4) was then calculated and thereaction free energy (ΔG) of reaction (5) was estimated. The free energy(ΔG) of reaction step 5 is difficult to determine experimentally orcomputationally because of charge separation issues. This free energywas estimated based on the fact that the ionization constant, Ka, ofmost carboxyl acids for such types of reactions fall in the range of10⁻⁴-10⁻⁵. Then, the free energy (ΔG) falls in the range of 7.8 to 9.2kcal/mol (Brown and Foote, 2002). In the case of reaction step 5, theaverage value of 8.5 kcal/mol was used. Then, the free energy ofreaction (2) becomes the algebraic sum of reactions 4 and 5. Theoptimized structure is shown in FIGS. 3a-b and the computational data ofthe reaction pathway given in the energy diagram are shown in Table 4.MEA-H⁺—CO₂ ⁻←→MEA-COOH  (4)MEA-COOH+H₂O←ΘMEA-CO₂ ⁻+H₃O⁺  (5)

In constructing the energy diagram in FIG. 3, it was attempted to obtainthe true transition state as the basis for all computations from amongpossibilities. The realisation that CO₂ stripping (reaction 1) involvesthe breaking of the N—C bond, allowed the calculations to be startedwith the stretching of the N—C bond. Then the transition state with (HF)was explored by applying HF/CPCM 6-31 G(d) level of theory. The detailedstructures (for the linear case) are shown in FIG. 3b , and the energiesare as listed in Table 4.

TABLE 4 Total (Hartree) and Relative (kcal mol⁻¹) of Energies of theStationary Points of Carbamate, Intermediates and Transition States forTwo Structures; solvent continuum (ε = 78.3), with CPCM methods Linear^(a) Circular HF/CPCM DFT/CPCM HF/CPCM DFT/CPCM 6-31G(d) 6-31G(d)6-31G(d) 6-31G(d) Intermediates MEA + CO₂ −396.7526219 −396.7515519Transition State −396.7370959 −396.7373374 Zwitterion (sp3) −396.7436287−396.7414147 MEACOOH −396.7658970 −396.7632555 MEA-CO₂ ⁻ + / / / / H₃O⁺Relative Energies ^(b) MEA + CO2 −9.74 −9.07 Transition State 0 −0.15Zwitterion (sp3) −4.10 −2.71 MEACOOH −18.07 −16.42 MEACOOH + H₂O →7.8-9.2 (8.5) ^(d) 7.8-9.2 (8.5) ^(d) MEA-CO₂ ⁻ + H₃O⁺ ^(c) MEA-CO₂ ⁻ +−9.57 −7.92 H₃O⁺ Ea ^(e) (Calc) 9.57 7.92 Ea ^(e) (exp) 13.65 ^(f); 9.87^(g) ^(a) The detailed structure is illustrated in FIG. 2. ^(b) We setthe transition state of linear structure at zero for the respectivelevel of theory ^(c) Reaction enthalpy of carbamate and proton is hardto estimate by experiments because decarboxylation of carbamate willoccur spontaneously with excess protons. ^(d) We took 8.5 kcal mol⁻¹ asthe average value of reaction energy because most acid ionizationconstants Ka of carboxyl acids fall within range of 10⁻⁴ to 10⁻⁵. Basedon pKa, we can calculate free energy ΔG. (Brown and Foote. 2002, OrganicChemistry 3^(rd) Ed, Harcourt College Publishers, Orlando, Fl.) ^(e) Thecomputational activation energy of CO₂ desorption under Zwitterionmechanism is the energy difference between transition state andcarbamate + H₃O⁺ as shown in FIG. 3a. ^(f) The latest experimental valueof CO₂ desorption is given by Jamal et al., 2006b. ^(g) The olderexperimental value from Rinker et al., 1996.

The data in Table 4 and FIG. 3 show that the total activation energy,E=E(TS)+ΔH1+ΔH2(exp) is about 10 kcal mol⁻¹. This value matches thosereportedly observed experimentally 13.65 and 9.87 kcal mol⁻¹ (Jamal, A.,Meisen, A., Lim, C. J., 2006. Chemical Engineering Science 61, 6590;Rinker, E. B., Ashour, S. S., Sandall, O. C., 1996. Kinetics andmodeling of carbon dioxide absorption into aqueous solutions ofdiethanolamine. Industrial Engineering Chemistry Research 35, 1107). TheZwitterion is a short lived intermediate for which the activation energyof desorption in the system should be the total desorption process ofreactions (1) and (2) rather than only reaction (1).

It is clear from FIG. 3 that the short lived Zwitterion is very unstableand disappears very quickly. The proton transfer goes backward to attachto MEA more easily rather than generating zwitterions. Also, even if theZwitterion is generated, it still requires some energy to overcome theenergy barrier. Theoretically, the zwitterions would prefer to stripprotons rather than break into MEA and CO₂, according to the potentialenergy surface diagram. This scenario creates difficulty in desorbingCO₂ from the absorbent without an external energy supply.

It appears a major reason for the difficulty in desorbing CO₂ from MEAloaded solution is the deficiency of protons. The MEA-H₂O—CO₂ solutionhas a pH value of 7-8 wherein limited liberated protons exist. Thus, theconcentration of H₃O⁺ is extremely low. The shortage of protons meansdesorption is unlikely to occur (estimated at one chance in 1-10million). Attempting to resolve these deficiencies results in therequirement for a large heat duty for CO₂ desorption.

While not wishing to be bound by theory, the present disclosure suggeststhat CO₂ desorption would be increased if the energy of the zwitterionwas lowered and/or if the new zwitterion was stabilized. For example,this might be achieved by introducing a proton such as H₃O⁺ into thesolution. One method of introduces a proton that will react with thecarbamate to facilitate CO₂ desorption would be to use an acid catalyst.Conversely, an alkaline catalyst would facilitate CO₂ absorption. Insummary, the energy diagram analysis suggests that the instability andshort-live intermediate Zwitterion and/or a shortage of proton insolution may be at least partially the cause of the requirement of anexternal heat supply for the CO₂ desorption process. Based on theproposed energy diagram, carbamate breakdown via Zwitterion mechanismmay utilize a proton-donating catalyst (e.g. Bronsted acid) to reducethe external heat requirement. On the absorption side, a Lewis base(electron donor) may facilitate CO₂ absorption.

CO₂ Desorption with a solid acid catalyst (Al Based Catalyst) wasanalysed. A computational simulation for MEA-COOH with Al(OH)₃ wasperformed with DFT/6-31 g(d) level of theory with CPCM model. Threecalculations were performed separately with the Al placed next to the Natom on (N—H), O atom on (O—H), and the other O atom, respectively. Theresults of these three sets of data show that the stability of thecomplex decreases in the order of O—Al>(OH)—Al>(NH)—Al (FIG. 4). FIG. 4shows that the N—Al connection is relatively weaker than O—Al bond sincethe N is saturated with three valance bonds (sp² hybridization) and thelone pair 2p orbital was already involved in the conjugation. However,the oxygen atom has a lone pair of orbitals in the N—CO₂ plane, whichcan bond to the Al easily. The 0 in (OH) is a weaker Lewis base than theoxygen (O) as shown by the computational data. This means that MEA-COOHwill attach to catalyst at the third oxygen atom (O). The third oxygenhas 3 advantages in the catalysis: 1) most likely to attach to Al (goodcapability of chemical absorption); 2) most stable configuration; 3)least stereo hindrance in both linear and circular structure because itis located at the end of the linear structure and outside the ring (FIG.4). Further simulation can estimate the energy difference betweenMEA-COOH—Al(OH)₃ and Zwitterion-Al(OH)₃ with same level of theory. TheAl atom is attached to the third oxygen. The energy difference is about5.4 kcal/mol, which is about 35% less than the difference withoutcatalyst 8.5 kcal/mol (FIG. 5). Therefore, the catalyst may help toreduce the reaction enthalpy for proton transfers by stabilizing theshort-live intermediate Zwitterion.

Based on FIG. 4, three potential active sites were identified on thecarbamate. The N and two oxygen atoms are Lewis base sites. These threeatoms (sites) may be used to facilitate CO₂ desorption via the followingsteps:

Step 0: Based on the structure of carbamate, the N atom is the keyposition for the CO₂ desorption process since desorption will notproceed unless the N—C bond breaks. The 0 anion is a very good protoncarrier, which can take a proton from an acid catalyst (e.g. HZSM-5catalyst) layer into the Al layer. The third 0 is a good catalystattachment center. The challenge is then to apply proper catalysisprocedure to take advantage of these centers, so as to facilitatedesorption.

Step 1: Carry Protons. The carbamate passes through HZSM-5 layer, over50% of carbamate will carry the protons and convert to MEA-COOH. Theseprotons are very useful for desorption.

Step 2: Chemisorption. The MEA-COOH reaches the Al layer. After externaland internal mass transfer, MEA-COOH attaches to the surface. O atombonds to Al as chemisorption takes place.

Step 3: Proton Transfer. The H on the oxygen dislocates the 0 and shiftsto the neighbouring N atom to construct Zwitterion. This is a slowendothermic reaction. Zwitterion-Al is still not stable but is betterthan Zwitterion without catalyst.

Step 4: N—C stretch. The H destroys the de-localized conjugation and N—Cbond starts to stretch.

Step 5: Bond breaking. The second Al attaches to N⁺ and helps to stretchthe N—C bond to facilitate desorption. The competition between the bondof Al—N with N—C may be important. This is also a slow, endothermic ratedetermining step (RDS) process. It is hard to go forward because the Alis unlikely to attach to N⁺ cation. However, since the N—C bond is weakand the N is neutral, and therefore, the connection is much stronger.This step is also the major difference between the catalyst mechanismand non-catalyst mechanism. Without an acid catalyst, the N—C bondbreaking relies only on external heat supply. However, with an acidcatalyst, the chemical bond helps as an additional molecular force topull the N—C bond. This sequence is shown in FIG. 5 which also comparesthe energy diagrams between the catalytic and non-catalytic approaches.

Step 6: Separation. N—C bond finally breaks and the Zwitterion splitsinto MEA and CO₂. Since the solubility of CO₂ in hot water is low, theCO₂ will detach from the catalyst easily and go to the gaseous phasesreadily. The desorption temperature may be in the range from 50 to 120°C. An increase in T increases the reaction speed, helps the CO₂ todetach from the catalyst as well as facilitate N—C bond breaking. Also,it weakens the attachment of MEA-COOH to catalyst. However, there is acost attached to a high temperature heat supply. Therefore, thetemperature for heat supply needs to be optimized to control the energycost.

Solid Base or Alkaline Catalyst for Absorption—From the reaction CO₂+2MEA→MEA-H⁺+MEA-COO⁻, the MEA-H⁺ will stay in the solution (H+ is fromthe N—H bond in another MEA when it converts to the carbamate). MEA-H⁺is not involved in the desorption process but it has low capability toabsorb CO₂ since the N is attached to a proton. Therefore, MEA-H⁺ has tobe converted to MEA to absorb CO₂ continuously. Conventional methods donot require this step because the higher T and heat duty would havealready stripped MEA-H⁺ to MEA. Since the energy cost is saved, the masscost cannot be neglected.

EXAMPLES Examples of Experiments Performed to Evaluate the Contributionof Acid Catalysts in CO₂ Stripping

Batch Tests on Catalytic Desorption of CO₂ from CO₂-Loaded MEA Solution

Several batch tests were performed on CO₂-loaded MEA solution withdifferent types of solid acid catalysts to obtain information on theireffectiveness and efficiency for CO₂ stripping. Two types of catalystswere used; a proton donor (Bronsted acid; e.g. H-ZSM-5) catalyst and anelectron acceptor (Lewis acid; e.g. γ-Al₂O₃) catalyst.

Experimental Setup:

The set up for the batch experiments is as shown in FIG. 6. It consistsof a heater and stirrer, a magnetic stirrer, a 600 mL glass bottle, athermocouple, a CO₂ gas mass flow meter (0-5 L/min), rubber cock,parafilm and tubing.

Materials and Chemicals:

The experiments were conducted using MEA (commercial grade, 99% purity)with molarity in range of 3-7 mol/L, CO₂ loading in the range of0.25-0.58 mol CO₂/mol MEA, temperature in the range of 50-92° C., twocatalysts; namely H-ZSM-5 and γ-Al₂O₃, and catalyst quantities ofH-ZSM-5: 25.0-65.0 g; γ-Al₂O₃ 25.0-50.0 g. The H-ZSM-5 and γ-Al₂O₃(commercial grade 99% purity) were sieved into approximately 2 mmaverage particle size.

Typical Experimental Run:

About 300 ml of the desired molarity of aqueous MEA solution wasprepared and placed in the bottle containing the desired weight of the 2mm particle size catalyst. The bottle also contained the magneticstirrer. The glass bottle was sealed with the rubber cock, which carriedthe thermocouple and rubber tubing. The rubber tubing was connected tothe CO₂ gas mass flow meter as shown in FIG. 7. Firstly, both thestirrer and the heater were turned on. Evolution of CO₂ started as thetemperature of the amine solution increased from room temperature toabout 92° C. The CO₂ flow rate was measured with the gas flow meterwhile temperature was measured with a thermocouple. The first data ofCO₂ flow rate was recorded at 50° C., and then subsequently every 5° C.until the system reached 92° C.

Experimental Apparatus.

A Desorption (Batch reactor) was shown in FIG. 6.

Examples of Experiments Performed to Evaluate the Contribution of Basicor Alkaline Catalysts in CO₂ Absorption

Semi-Batch Tests on Catalytic Absorption of CO₂ in CO₂-Lean MEA Solution

Several sets of tests were performed on lean MEA solution with solidbase catalysts to evaluate their performance in terms of efficiency andkinetics. MgCO₃ (5.0 to 15.00 g) was used as an example of the solidbase or alkaline catalyst that can accelerate CO₂ absorption as comparedto conventional absorption (i.e. non-catalytic absorption).

Experimental Set-Up

The experimental set-up was as shown in FIG. 7. The apparatus consistedof a centrifuge pump, mass flow meter, a K-type gas cylinder withregulator, a 600 mL beaker, a 500 mL three-neck round glass bottle, aglass condenser (12/20 type), another glass condenser used as anabsorption column (internal diameter ⅝ inch, 24/40 type), several glassvacuum adaptors (connectors and angles of 105, 90 bent hose connector,all with 24/40 type), rubber cocks, parafilm and tubing, a plastic3-port valve (T-shaped) with a plastic fitting cock, and glass wool(10-15 g). Other requirements for the experiments were a graduatedcylinder (500 ml), pipette (5 ml), thermocouple, gas mass flow meter(0-5 L/min), CO₂ concentration analyzer (0-20%), and a timer. Athermometer is fitted through the small hole to measure the temperatureof the solution.

Typical Experimental Run

The set-up was built as shown in FIG. 7. All the connections wereproperly sealed so as to avoid gas leakage. A small amount (3-4 g) ofglass wool was then placed at the bottom end of the absorber to supportthe catalyst. The liquid condenser (12/20) in the right line was filledwith cold water and sealed at both exits with parafilm. The MEA solutionwas pre-loaded with CO₂ to the desired CO₂ loading. The initial loading,temperature of the lean MEA solution, initial gas flow rate and theconcentration of CO₂ in the inlet gas were recorded. These initialconditions for all experiments were made as close as possible to eachother in order to be able to compare the results.

Firstly the mixed gas was introduced at the desired flow rate to flowthrough the absorber and coming out at the CO₂ analyzer outlet where theoutlet (off gas) was measured. At this point the CO₂ concentration inthe inlet gas was the same as the outlet CO₂ concentration. Then, MEAsolution was pumped and introduced into the absorption column at the topposition through a condenser at the desired temperature and flow rate.Then, the bottom of the 3-port valve (T shape) was closed with plasticcock to seal the whole process. Then the timer was started and data wererecorded every 5 seconds including the temperature of amine in thestorage bottle and the CO₂ gas concentration. The temperature of theamine increases and the CO₂ concentration decreases gradually because ofCO₂ absorption. The process continued for about 5 minutes after whichthe pump was stopped and the mixed gas flow shut off. The volume of theamine collected in the storage bottle was determined with the graduatedcylinder. Then, CO₂ loading of the rich MEA was also determined bytitration using a Chittick apparatus. Finally, all the data arecollected and the curve of CO₂ concentration vs. time can be drawn forthe kinetic study.

Examples of Experiments Performed to Evaluate the Contribution of AcidCatalysts for CO₂ Stripping and Basic or Alkaline Catalysts for CO₂Absorption in an Example of an Amine-Based Post Combustion CO₂ CaptureProcess Configuration

Four sets of tests were performed on an example of a steady state CO₂capture process involving CO₂ absorption and CO₂ desorption usingdifferent combinations of catalyst or no catalyst in the stripper andcatalyst or no catalyst in the absorber in order to evaluate theindividual contributions of the individual catalysts. These were: (a)solid alkaline catalyst in the absorber and solid acid catalyst in thestripper, (b) no catalyst in the absorber and no catalyst in thestripper, (c) no catalyst in the absorber but a solid acid catalyst inthe stripper, and (d) a solid alkaline catalyst in absorber but nocatalyst in the stripper. The performance of the catalysts in the fourscenarios was evaluated in terms of CO₂ absorption kinetics heat dutyand desorption temperature.

Experimental Setup

The process configuration of the experimental setup was as shown in theschematic illustrated in FIG. 8. It consisted of two columns each ofabout 1000 mm in height. The top column was the absorber column (1.9 mmOD and 1.61 mm ID) which was bolted on top of the stripper column (2.375mm OD and 2.967 mm ID) using flanges without any direct flow throughbetween the two columns at the flanged section. For the absorber column,there are ports for gas inlet, off gas outlet, lean amine inlet and richamine outlet. On the other hand, the stripper has ports for the richamine inlet, lean amine outlet and CO₂ product outlet. The CO₂ productoutlet flow passes through an ice bath to trap condensable vapors so asto allow only CO₂ gas to pass through the mass flow meter which measuredthe CO₂ production rate. On the other hand, the rich amine from theabsorber column passes through a stainless steel plate type heatexchanger with the heating fluid being steam or hot water (depending onthe desired rich amine inlet temperature to the stripper column) beforeentering the stripper column. The lean amine from the stripper passesthrough a solid base or alkaline catalyst in order to neutralize thelean amine coming out of the stripper before being cooled in an ice bathto the desired temperature, and before being pumped to the absorbercolumn. Both the absorber and stripper columns each had about 5thermocouple ports placed at about 150 mm spacing along the length ofthe columns in order to measure the temperature profile along thecolumns.

A typical experimental run involved introducing the desired amount ofthe desired catalyst solid acid catalyst into the stripper and also thedesired amount of the desired base or alkaline catalyst into theabsorber. With the catalysts in place, and the setup assembled as shownin FIG. 8, the amine (e.g. MEA) solution of the desired molarity ispumped from the amine storage bottle and introduced in the absorbercolumn through the top port and is circulated at the desired steadystate flow rate. Then steam or hot water is introduced in the heatexchanger in co-current mode with the rich amine flow which is heated toabout 96° C. Steady state was achieved after about 45-60 min after whichthe gas mixture of known CO₂ concentration (e.g. 13% CO₂ concentration,balance nitrogen) of the desired flow rate (e.g. 1.8 L/min) wasintroduced into the absorber column through the bottom port as shown inthe figure. The whole process takes about 120 minutes during which time(i.e. after steady state had been reached) the rich amine loading, leanloading, temperature profiles of both stripper and absorber columns, CO₂concentration in the off-gas, steam or hot water rate and temperature,and CO₂ product rate were measured. The results are shown in Tables10-13 a-d for the four scenarios. It should be noted that any scenarioswhere the solid acid catalyst is contained in the stripper also includespossibilities where the solid acid catalyst is contained in unitsadjacent to the stripper such as tubes and/or lines and/or pipes and/orvessels that exit or enter the stripper column or are close to thestripper column for which there is any CO₂ desorption. Similarly, thescenarios where the solid alkaline catalyst is contained in the absorberalso includes the possibilities where the catalyst is contained in unitsadjacent to the absorber such as tubes and/or lines and/or pipes and/orvessels that exit or enter the absorber column or are close to theabsorber column for which there is contact of the CO₂ containing gas(e.g. flue gases, reformate gas, natural gas, etc.) with the liquidabsorbent.

Results of the Experimental Evaluation of the Contribution of AcidCatalysts in CO₂ Stripping

Effect of the Presence of Proton Donor Solid Acid Catalyst (HZSM-5)

The results showing the contribution of proton donor solid acid catalyst(H-ZSM-5) are given in Table 5 as well as in FIG. 9. It is clear fromboth Table 5 and FIG. 9 that without the catalyst, there is nodesorption of CO₂ from the loaded amine up to 75° C., and negligible CO₂desorption from 75 to 95° C. This shows that, at these temperatures,using the thermal process alone, it is difficult to strip CO₂ fromloaded amine because of the high activation energy involved in theprocess in addition to the deficiency in protons. In the presence of theproton donor solid acid catalyst, the results show that there is CO₂desorption and the rate of CO₂ desorption increases with temperatureeven at temperatures below 92° C. (which is well below the conventionalstripping temperature for a purely thermal process). CO₂ stripping atthis low temperature can be attributed to the presence of protonsintroduced by the proton donor solid acid catalyst. The increase in theproton concentration in the system decreases the activation energyrequired for stripping, and therefore shifts the mechanism or pathway infavor of the one with a lower activation energy which facilitates CO₂stripping for this highly endothermic process. In order to directly showthat a higher concentration leads to a higher desorption rate, weconducted a number of CO₂ desorption experiments with different amountsof the proton donor solid acid catalyst. The results are also given inTable 5 and FIG. 9. It can be seen from these results that the higherthe amount of proton donor solid acid catalyst, the higher the CO₂desorption rate and the lower the temperature CO₂ desorption starts.These results confirm that a higher amount of protons in the desorptionsystem causes a bigger decrease in the activation energy required forCO₂ stripping.

TABLE 5 Desorbed CO₂ Flow Rate (L/min) for 300 ml of Rich MEA Solution(5M, α = 0.45) for Different Amounts of H-ZSM-5 (g) F_(CO2) Mass ofH-ZSM-5 (g) T/° C. 0 25.0 37.5 50.0 65 50 0.00 0.00 0.00 0.00 0.01 550.00 0.00 0.00 0.00 0.01₅ 60 0.00 0.00 0.01 0.01 0.02 65 0.00 0.00 0.010.01 0.03 70 0.00 0.00 0.01 0.02 0.04 75 0.00 0.00 0.01 0.02 0.04 800.01 0.01 0.01 0.03 0.05 85 0.01 0.02 0.02 0.04 0.07 90 0.01 0.05 0.060.14 0.12 92 0.01 0.10 0.11 0.18 0.16Effect of Amine Molarity

The effect of the amine molarity on CO₂ desorption rate is illustratedin Table 6 as well as FIG. 10. The results show that starting from thesame CO₂ rich loading (e.g. 0.455 mol CO₂/mol MEA), there is only aslight increase in CO₂ desorption rate with MEA molarity. Thus, thecontribution of MEA molarity to CO₂ desorption rate is small providedthere is sufficient amount of protons introduced in the system from theproton donor solid catalyst. It can also be observed from the resultsthat a combination of high CO₂ loading (0.577 mol CO₂/mol MEA) and highmolarity (7 mol/L MEA) results in a benefit in that a high rate ofdesorption of CO₂ is obtained and it starts at a very low temperature(<50° C.).

TABLE 6 Desorbed CO₂ Flow Rate (L/min) for 300 ml of Rich MEA Solutionwith 65.0 g H-ZSM-5 for Various Molarities and Loading F_(CO2) MEAsolution with different Loading T/° C. 3M (0.455) 5M (0.455) 7M (0.577)^(a) 50 0.01 0.01 0.13₅ 55 0.01 0.01₅ 0.16 60 0.02₅ 0.02 0.17 65 0.02₅0.03 0.17 70 0.03 0.04 0.18 75 0.03₅ 0.04 0.17 80 0.05 0.05 0.18 85 0.060.07 0.18 90 0.09 0.12 0.19 92 0.11 0.16 0.18 ^(a) 7M MEA solution isover loaded (>0.5).Effect of CO₂ Loading in Rich Amine

The specific contribution of CO₂ loading to CO₂ stripping in thepresence of the proton donor catalyst is shown in Table 7 as well as inFIG. 11. The results show clearly that there are positive benefits froma high CO₂ loading in the rich amine resulting in increased rate of CO₂desorption.

TABLE 7 Desorbed CO₂ Flow Rate (L/min) for 300 ml of Rich MEA Solution(5M) with 65.0 g HZSM-5 Catalyst for Various Loadings and TemperaturesLoading (α) T/° C. 0.248 0.296 0.348 0.382 0.455 50 0.00 0.00 0.00 0.000.01 55 0.00₅ 0.00₅ 0.00₅ 0.00₅ 0.01₅ 60 0.01₅ 0.01₅ 0.01 0.01 0.02 650.02 0.01₅ 0.01 0.01 0.03 70 0.02 0.02 0.02 0.02 0.04 75 0.03₅ 0.03₅0.02₅ 0.02₅ 0.04 80 0.04₅ 0.05 0.03₅ 0.03 0.05 85 0.05 0.05₅ 0.04 0.04₀0.07 90 0.05 0.06 0.05 0.05₅ 0.12 92 0.07 0.06₅ 0.05 0.07 0.16Effect of Type of Acid Catalyst

In these experiments, we compared two types of solid acid catalysts: (a)a proton donor catalyst (e.g. HZSM-5) and an electron acceptor catalyst(e.g. γ-Al₂O₃) for their effects on CO₂ desorption from CO₂ loaded richMEA solutions. The molarity of MEA was 5 mol/L and the CO₂ loading was0.45 mol CO₂/mol MEA. The results are given in Table 8 as well as inFIG. 12. The results for CO₂ desorption without any catalyst are alsoshown for comparison. It can be seen that for the same amount ofcatalyst at any desorption temperature, the proton donor solid acidcatalyst are better than the electron acceptor solid acid catalyst asthere are higher CO₂ desorption rates when the proton donor solidcatalysts are used as compared to the electron acceptor catalysts. Also,for each catalyst, the CO₂ desorption increases with the amount ofcatalyst used. There is negligible CO₂ desorption when no catalyst isused as mentioned earlier.

TABLE 8 Desorbed CO₂ Flow Rate (L/min) for 300 ml of Rich MEA Solution(5M, α = 0.45) for Different Types of Solid Acid Catalysts (Proton DonorSolid Acid Catalyst (HZSM-5) and Electron Acceptor Solid Acid Catalyst(γ-Al₂O₃) T/ F_(G0) HZSM-5 γ-Al₂O₃ ° C. No Cata 25.0 g 37.5 g 50.0 g25.0 g 37.5 g 50.0 g 50 0.00 0.00 0.00 0.00 0.00 0.00 0.00 55 0.00 0.000.00 0.00 0.00 0.00 0.00 60 0.00 0.00 0.01 0.01 0.00 0.01 0.01 65 0.000.00 0.01 0.01 0.00 0.01 0.01 70 0.00 0.00 0.01 0.02 0.00 0.01₅ 0.01₅ 750.00 0.00 0.01 0.02₅ 0.01 0.01₅ 0.02 80 0.01 0.01 0.01 0.03 0.01 0.020.03₅ 85 0.01 0.02 0.02 0.04₅ 0.01₅ 0.02 0.04 90 0.01 0.05 0.06 0.140.01₅ 0.02₅ 0.05₅ 92 0.01 0.10 0.11 0.18 0.03₅ 0.06Results of the Experimental Evaluation of the Contribution of Basic orAlkaline Catalysts in CO₂ Absorption

The effect of a solid alkaline catalyst in the absorber on CO₂absorption is illustrated in Table 9 as well as FIG. 14. The resultsshow the concentration of the gas mixture coming out of the absorbercontaining either a solid alkaline catalyst of different amounts or withno catalyst. There is a clear distinction between the runs withcatalysts and the one without catalyst. As can be seen, the CO₂concentration in the off-gas decreases more rapidly with catalyst thanwithout catalyst indicating more rapid absorption of CO₂ with catalystthan without catalyst. Within the limits of amounts used for theexperiment, the amount of catalyst does not seem to produce anysignificant change in the CO₂ absorption rate.

TABLE 9 Concentration of CO₂ in the Outlet gas for Different amounts ofMgCO₃ Amount of Catalyst Time No Catalyst 5.0 g 10.0 g 15.0 g 0 12.512.6 12.3 12.7 5 11.5 12.1 11.2 10 12.5 9.6 10.5 9.0 15 7.0 7.3 7.3 2011.2 4.8 5.2 5.8 25 3.4 4.0 3.7 30 8.8 2.3 3.1 2.7 35 1.2 1.9 2.0 40 5.51.0 1.2 1.6 45 0.8 1.0 1.4 50 3.0 0.7 0.7 1.2 55 0.6 0.7 1.1 60 1.5 0.60.6 1.0 65 0.5 0.6 1.0 70 0.8 0.5 0.6 0.9 75 0.5 0.6 0.9 80 0.5 0.4 0.60.9 85 0.4 0.6 0.9 90 0.4 0.4 0.6 0.9 100 0.3 0.4 0.6 0.9 110 0.3 0.40.6 0.9 120 0.3 0.4 0.6 0.9 130 0.3 0.4 0.6 0.9 140 0.3 0.4 0.6 0.9 1500.3 0.4 0.6 0.9 160 0.3 0.4 0.6 0.9 170 0.3 0.4 0.6 0.9 180 0.3 0.4 0.60.9 190 0.3 0.4 0.6 0.9 200 0.3 0.4 0.6 0.9 210 0.3 0.4 0.6 0.9 220 0.30.4 0.6 0.8 230 0.3 0.4 0.6 0.8 240 0.3 0.4 0.6 0.8 250 0.3 0.4 0.6 0.8260 0.3 0.4 0.6 0.8 270 0.3 0.4 0.6 0.8 280 0.3 0.4 0.6 0.8 290 0.3 0.40.6 0.8 300 0.3 0.4 0.6 0.8 F_(G0), F_(L0) (L/min) 1.81; 0.13 1.91; 0.121.76; 0.11 1.75; 0.12 V of MEA (ml) 400 365 360 370 Initial α 0.1710.151 0.167 0.177 Final α 0.237 0.196 0.236 0.232 Inlet gas is premixedCO₂ (13%) with N₂; Inlet Liquid is lean MEA solutionExperimental Evaluation of the Contribution of an Acid Catalyst for CO₂Stripping and Basic or Alkaline Catalysts in CO₂ Absorption in anExample of an Amine-Based Post Combustion CO₂ Capture ProcessConfiguration

Results were collected from four sets of tests performed on a steadystate CO₂ capture process involving CO₂ absorption and CO₂ desorptionusing different combinations of catalyst or no catalyst in the stripperand catalyst or no catalyst in the absorber in order to evaluate theindividual contributions of the individual catalysts. These were: (a)solid alkaline catalyst in the absorber and solid acid catalyst in thestripper, (b) no catalyst in the absorber and no catalyst in thestripper, (c) no catalyst in the absorber but a solid acid catalyst inthe stripper, and (d) a solid alkaline catalyst in absorber but nocatalyst in the stripper. The performance of the catalysts in the fourscenarios was evaluated in terms of CO₂ absorption kinetics heat dutyand desorption temperature. These are shown in Tables 10, 11, 12 and 13,respectively. The rate of CO₂ desorption is shown as F_(CO2) (L/min) asmeasured by the flow meter while the rate of absorption is given asF_(CO2abs). The results in Table 10 show a rapid absorption of CO₂ and asubstantial desorption of CO₂ when the alkaline solid catalyst and thesolid acid catalysts are used simultaneously in the absorber andstripper, respectively in a continuous steady state process. The heatduty obtained under this condition was 1.56 GJ/tonne of CO₂ produced.The heat supply was calculated based on the heat balance around thestripper shown in FIG. 8 whereas the CO₂ produced was as measured by theflowmeter and was comparable with the value obtained by lean amine-richamine difference. The heat duty obtained in this process represents animprovement when compared with the fact that the best reported heat dutyusing the same absorbent (5 molar MEA) without the catalyst is 2.58GJ/tonne CO₂ produced (PCT/CA2008/001029). In the case where there is nocatalyst in the absorber and no catalyst in the stripper, Table 11 showsthat there is absorption in the absorption column but the CO₂ desorptionrate is negligible. The reason is that the activation energy forstripping is too high and the temperature of operation is not able tosupply this large external heat. There is absorption without catalystbut the rate is not as rapid as with the alkaline catalysts.

With the solid acid catalyst only in the stripper column, Table 12 showsthat there is substantial desorption of CO₂ similar to first case ofTable 10 (where there was catalyst in both columns. Table 12 shows thatthe rich loading for the case of the solid catalyst only in the stripper(0.389 mol CO₂/mol MEA) was lower than the rich loading for the case(Table 10) where there was catalyst in both columns (0.422 mol CO₂/molMEA) for corresponding experimental times. This demonstrates that thepresence of the solid alkaline catalyst facilitated absorption leadingto much higher CO₂ absorption rates. In the case where there is a solidalkaline catalyst in the absorber (Table 13), the results for CO₂desorption are equivalent to the case given in Table 11 which also didnot contain a catalyst in the stripper column. Therefore a solid acidcatalyst is crucial in reducing the activation energy for CO₂ desorptionbecause it provides the protons necessary to shift the equilibriumtowards a lower temperature CO₂ desorption thereby minimizing theexternal energy supply. On the other hand, a solid alkaline catalyst isrequired in the absorber to increase the rate of absorption resulting ina higher CO₂ rich loading. This high absorption rate reduces the size ofthe absorption column.

TABLE 10 Steady State Flow process of CO₂ absorption and desorption withcatalysts in both column.^(a) F_(CO2) F_(CO2) Fl Fg^(b) Fl/Fg timeF_(CO2) des^(c) abs Rich Lean T0 T1 T2 L/min L/min L/mol min X % % L/minL/min L/min loading loading Degree 0.10 1.8 1.25 120 1.5 0.14-0.24 0.1900.216 0.384 0.371 45.7 54.0 53.9 150 1.6 0.15-0.24 0.195 0.214 0.4040.385 42.5 49.0 48.5 180 1.4 0.15-0.25 0.200 0.218 0.419 0.390 44.8 50.751.1 200 1.4 0.15-0.25 0.200 0.218 0.422 0.399 44.9 50.6 50.9 Fl Fg^(b)Fl/Fg time T3 T4 T6 T7 T8 T9 T10 T_(steam) T5_(HE) L/min L/min L/mol minDegree 0.10 1.8 1.25 120 54.8 54.3 95.1 94.0 93.3 93.1 92.9 100.7 97.4150 49.1 48.7 94.8 93.6 93.2 92.9 92.5 100.7 97.3 180 52.5 51.7 95.093.8 93.3 92.9 91.8 100.7 97.3 200 52.0 51.2 95.0 93.8 93.3 92.8 92.5100.7 97.3 ^(a)50.0 g of CaCO₃ mixed with glass marbles introduced inthe absorber and 120.0 g H-ZSM-5 mixed with 790 g α-Al₂O₃ introduced inthe stripper. ^(b)The CO₂ concentration of mixed gas is 13.5%, balanceN₂. ^(c)Average value read from gas flow meter Heat Duty = 1.56 GJ/tonneof CO₂ produced

TABLE 11 Steady State Flow process for CO₂ absorption and desorptionwith no catalysts in either column.^(a) F_(CO2) F_(CO2) Fl Fg^(b) Fl/Fgtime F_(CO2) des abs Rich Lean T0 T1 T2 L/min L/min L/mol min X % %L/min L/min L/min loading loading Degree 0.10 1.0 2.25 0 N/A −0.05~0.020.000 0.000 N/A N/A 30.1 38.0 36.9 30 0.2 −0.08~0.04 0.000 0.140 N/A N/A46.2 58.7 58.2 60 0.3 −0.08~0.05 0.000 0.139 N/A N/A 46.6 57.4 56.7 0.101.8 1.25 90 0.4 −0.09~0.04 0.000 0.248 N/A N/A 46.5 55.7 55.5 120 0.4−0.08~0.04 0.000 0.248 0.313 0.330 46.6 55.9 55.6 150 0.7 −0.08~0.050.000 0.243 0.348 0.357 46.1 54.6 54.6 180 0.9 −0.05~0.06 0.045 0.2390.402 0.398 44.7 53.5 53.6 200 1.4 −0.05~0.08 0.088 0.230 0.419 0.41245.7 56.1 55.3 Fl Fg^(b) Fl/Fg time T3 T4 T6 T7 T8 T9 T10 T_(steam)T5_(HE) L/min L/min L/mol min Degree 0.10 1.0 2.25 0 34.6 34.0 92.5 82.076.5 74.2 67.4 100.2 97.0 30 56.5 55.6 94.8 79.3 86.3 85.8 85.7 101.197.9 60 54.8 54.2 94.8 87.3 87.6 86.5 85.2 101.2 97.9 0.10 1.8 1.25 9054.6 55.3 94.8 79.9 85.5 86.2 84.8 101.3 97.9 120 53.6 54.2 95.9 81.086.4 86.2 85.2 101.2 97.9 150 53.3 54.2 95.9 90.1 89.8 87.6 85.4 101.297.8 180 52.5 53.1 94.8 92.1 92.0 90.7 89.4 100.6 97.3 200 53.6 52.594.8 93.5 93.0 91.9 90.5 100.8 97.5 ^(a)Absorber is packed with inertglass marbles and stripper is packed with inert beads ^(b)The CO₂concentration of mixed gas is 14.2%, balance N₂.

TABLE 12 Steady State Flow process for CO₂ absorption and desorptionwith catalysts in stripper only.^(a) F_(CO2) F_(CO2) Fl Fg^(b) Fl/Fgtime F_(CO2) des^(c) abs Rich Lean T0 T1 T2 L/min L/min L/mol min X % %L/min L/min L/min loading loading Degree 0.10 1.8 1.25 120 2.2 0.08-0.190.135 0.216 0.362 0.357 48.6 62.9 61.4 150 2.5 0.12-0.20 0.175 0.2110.378 0.362 53.9 63.5 63.2 180 2.4 0.14-0.22 0.180 0.212 0.384 0.35752.4 61.9 61.5 200 2.4 0.14-0.23 0.185 0.212 0.389 0.362 51.7 61.1 60.8Fl Fg^(b) Fl/Fg time T3 T4 T6 T7 T8 T9 T10 T_(steam) T5_(HE) L/min L/minL/mol min Degree 0.10 1.8 1.25 120 58.7 58.0 95.4 94.4 94.3 93.7 93.5100.7 97.4 150 61.9 62.3 95.2 94.1 94.1 93.9 93.5 100.6 97.3 180 60.761.3 95.1 94.1 94.1 93.8 93.4 100.6 97.3 200 59.2 60.4 95.2 94.1 94.093.8 93.3 100.6 97.3 ^(a)Absorber packed with glass marbles and Stripperpacked with 120.0 g H-ZSM-5 mixed with 790 g α-Al₂O₃. ^(b)The CO₂concentration of mixed gas is 14.2%, balance N₂. ^(c)Averaged value readfrom gas flow meter

TABLE 13 Steady State Flow process for CO₂ absorption and desorptionwith catalysts in absorber only.^(a) F_(CO2) F_(CO2) Fl Fg^(b) Fl/Fgtime F_(CO2) des^(c) abs Rich Lean T0 T1 T2 L/min L/min L/mol min X % %L/min L/min L/min loading loading Degree 0.10^(d) 1.0 2.25 0 N/A N/A N/AN/A N/A N/A 24.3 23.8 23.8 30 1.6  0.00~0.03 0.000 0.126 N/A N/A 26.129.1 29.7 60 1.7 0.000 0.000 0.123 N/A N/A 43.4 52.2 53.0 0.10 1.8 1.2590 1.8 −0.02~0.03 0.000 0.223 N/A N/A 43.1 52.7 53.3 120 2.0 −0.03~0.050.000 0.220 0.383 0.392 43.6 51.1 51.5 150 2.2 −0.03~0.05 0.000 0.2160.391 0.411 44.3 51.2 51.4 180 2.3 −0.03~0.05 0.000 0.214 0.400 0.41145.3 52.9 52.8 200 2.5 −0.04~0.09 0.050 0.211 0.419 0.415 45.9 53.6 54.10.10^(e) 1.8 1.25 30 2.0 −0.04~0.08 0.000 0.220 0.417 0.417 40.8 51.351.5 60 2.2 −0.06~0.08 0.050 0.216 0.427 0.422 46.7 56.9 57.3 90 2.4−0.06~0.08 0.093 0.212 0.431 0.423 48.8 57.1 57.5 120 2.5 −0.08~0.110.100 0.211 0.431 0.422 49.5 57.1 57.7 Fl Fg^(b) Fl/Fg time T3 T4 T6 T7T8 T9 T10 T_(steam) T5_(HE) L/min L/min L/mol min Degree 0.10^(d) 1.02.25 0 23.6 23.4 21.2 19.5 19.5 19.5 19.5 22.8 23.6 30 26.7 26.0 95.091.4 90.4 88.4 71.3 100.4 97.2 60 51.7 50.8 95.0 92.1 91.2 90.3 89.7100.4 97.1 0.10 1.8 1.25 90 52.4 52.2 94.9 92.4 92.1 91.3 90.8 100.497.1 120 51.5 51.7 94.6 92.0 91.8 90.8 90.3 100.3 97.0 150 51.0 50.894.3 91.9 91.6 90.3 90.0 100.4 97.0 180 52.4 52.3 94.6 92.5 92.5 91.591.2 100.4 97.0 200 53.7 53.7 94.6 92.5 92.2 91.5 91.1 100.3 97.00.10^(e) 1.8 1.25 30 51.6 46.7 94.8 92.5 92.1 91.5 91.2 100.5 97.3 6056.8 57.1 95.0 93.0 92.7 92.4 91.8 100.5 97.2 90 57.0 57.3 94.9 93.293.1 92.7 92.3 100.6 97.2 120 57.3 57.6 95.2 93.3 93.2 92.8 92.4 100.697.3 ^(a)50.0 g of CaCO₃ mixed with glass marbles are packed in absorberand stripper is packed with inert beads ^(b)The CO₂ concentration ofmixed gas is 14.2%, balance N₂. ^(c)The loading (α) at 120 and 180 minshowed the lean amine is richer than “rich” amine, which means nodesorption occurs itn stripper at all. Therefore, the desorption rate offirst 90 minutes can be regarded as zero. ^(d)Steam rate of 1.20-1.35kg/h ^(e)Steam rate of 3.0-3.20 kg/h

In the present disclosure we used computational and experimentalestimates to construct an energy diagram that describes the CO₂desorption or carbamate breakdown process accurately. The analysis ofthe energy diagram shows that the large heat requirement for CO₂desorption (i.e. carbamate breakdown) may be due to insufficient protonsin the system and/or the lack of stabilization of the zwitterions.

The present disclosure provides for a system comprising a chemicalcontribution for CO₂ absorption and CO₂ desorption. The chemicalcontribution may take the form of a solid acid catalyst which providesprotons in the stripping process (e.g. in the stripper column) therebystabilizing the zwitterions. This stabilization may reduce the energyrequired for CO₂ desorption. The chemical contribution may allow for thetemperature of the heat supply medium for CO₂ desorption to start at aslow as 50° C. and go up to 160° C., if desired.

The chemical contribution may comprise a solid alkaline catalyst whichprovides electrons in the absorber thereby increasing the rate of CO₂absorption. This may allow for a reduced absorber column. Or extend theuseful life of current equipment. Or allow for better removal of CO₂from gas streams.

When using a solid acid catalyst in the stripper and a solid alkalinecatalyst in the absorber the heat duty may be approximately 1.56GJ/tonne CO₂ produced. This represents a tremendous improvement whencompared with the best heat duty (2.58 GJ/tonne CO₂ produced) using thesame absorbent (5 molar MEA) but without catalyst in both the stripperand absorber.

It is believed that the higher the amount of proton donor solid acidcatalyst in the stripper column, the higher the CO₂ desorption rate andthe lower the temperature CO₂ desorption starts. These results confirmthat a higher amount of protons in the desorption system causes a biggerdecrease in the activation energy required for CO₂ stripping.

Our results show that a combination of high CO₂ loading (e.g. 0.577 molCO₂/mol MEA) and high molarity (e.g. 7 mol/L MEA) results in a benefitin that a high rate of desorption of CO₂ is obtained and it starts at alower temperature (<50° C.).

There appears to be a superior performance of the proton donor catalystover the electron acceptor catalysts which may be explained on the basisthat CO₂ desorption from loaded CO₂ requires addition of protons ratherthan withdrawal of electrons. The proton donation step in the desorptionmechanism alters the mechanism or pathway in favor of lowering theactivation energy for CO₂ desorption. This may explain the beneficialeffect of the proton donor catalyst over that of the electron acceptorcatalyst even though both are acid catalysts.

The alkaline catalyst in the stripper can increase the rate of CO₂absorption in the lean amine.

The present disclosure can be applied to other amine based or ammoniabased methods for CO₂ absorption and desorption. This includes usingdifferent types of amines and/or absorbents, different processconfigurations, and using steam and/or hot water to provide the energythat is required for stripping for CO₂ capture from flue gas streams,natural gas, reformate gas, etc. In addition, with proper selection ofthe catalyst type, the device can also be used for catalyticdistillation.

The acid catalyst may be contain in the stripper and/or may also becontained in units adjacent to the stripper such as tubes and/or linesand/or pipes and/or vessels that exit or enter the stripper column orare close to the stripper column for which there is any CO₂ desorption.

The alkaline catalyst may be contained in the absorber and/or may alsobe contained in units adjacent to the absorber such as tubes and/orlines and/or pipes and/or vessels that exit or enter the absorber columnor are close to the absorber column for which there is contact of theCO₂ containing gas (e.g. flue gases, reformate gas, natural gas, etc.)with the absorbent.

The device can be applied to catalytic distillation, rectification, andany process that separates a component or components frommulti-component streams.

REFERENCES

-   Brown and Foote, 2002. Organic Chemistry 3^(rd) ed., Harcourt    College Publishers, Orlando, Fla.-   Idem, R., Wilson, M., Toniwachwuthikul, P., Chakma, A., Veawab, A.,    Aroonwilas, A., Gelowitz, D., 2006. Pilot Plant Studies of the CO₂    Capture Performance of Aqueous MEA and Mixed MEA/MDEA Solvents at    the University of Regina CO₂ Capture Technology Development Plant    and the Boundary Dam CO₂ capture Demonstration Plant. Ind. Eng.    Chem. Res. 45, 2414-   Yagi, Y., Mimura, T., Iijima, M., Ishida, K., Yoshiyama, R.,    Kamijio, T., Yonekawa, T., 2005. Improvements of Carbon Dioxide    Capture Technology from Flue Gas. 7th International Conference on    Greenhouse Gas Control technologies, 5-9 Sep. 2004, Vancouver,    Canada.

In the description that follows, a number of terms are used, thefollowing definitions are provided to facilitate understanding ofvarious aspects of the disclosure. Use of examples in the specification,including examples of terms, is for illustrative purposes only and isnot intended to limit the scope and meaning of the embodiments of theinvention herein. Numeric ranges are inclusive of the numbers definingthe range. In the specification, the word “comprising” is used as anopen-ended term, substantially equivalent to the phrase “including, butnot limited to,” and the word “comprises” has a corresponding meaning.

It is contemplated that any embodiment discussed in this specificationcan be implemented or combined with respect to any other embodiment,method, composition or aspect of the invention, and vice versa.

All citations are herein incorporated by reference, as if eachindividual publication was specifically and individually indicated to beincorporated by reference herein and as though it were fully set forthherein. Citation of references herein is not to be construed norconsidered as an admission that such references are prior art to thepresent invention.

The invention includes all embodiments, modifications and variationssubstantially as hereinbefore described and with reference to theexamples and figures. It will be apparent to persons skilled in the artthat a number of variations and modifications can be made withoutdeparting from the scope of the invention as defined in the claims.Examples of such modifications include the substitution of knownequivalents for any aspect of the invention in order to achieve the sameresult in substantially the same way.

The invention claimed is:
 1. A process for separating at least a portionof an acid gas from a gaseous mixture, said process comprising: a.contacting the gaseous mixture with an absorption medium wherein saidmedium absorbs at least a portion of the acid gas to form a rich medium;and b. separating at least a portion of the acid gas from the richmedium to form a lean medium; wherein the absorption step is performedin the presence of a heterogeneous alkaline catalyst and the separationstep is performed in the presence of a heterogeneous proton donor acidcatalyst, wherein the heterogeneous alkaline catalyst is not present instep b, and the heterogeneous proton acid donor catalyst is not presentin step a, wherein: the acid gas is carbon dioxide; the absorptionmedium is an amine; the heterogeneous proton donor acid catalyst isselected from heteropoly acids (HPAs), silica-supported Nafion (SAC-13),alumina, amorphous silica-alumina, molecular sieves, mesoporousaluminosilicates, clays, pillared clays (PILC), and acidic porous clayheterostructures (PCH), and combinations thereof; and the heterogeneousalkaline catalyst is selected from Na/NaOFi/AkCk, quaternary ammoniumfunctionality supported over a resin (A26), quaternary ammonium saltfunctionalized silica gel, ZnO, ZrCh, Tl1O2, TiCk, CaO, MgO, MgCCk, SrO,BaO, Na metal dispersed on Al2O3, Na/MgO, La203, Y2O3, alkali metaloxides, alkali metal ions on alumina, alkali metal ions on silica,alkali metal on alkaline earth oxide, alkali metals and alkali metalhydroxides on alumina, basic clay minerals, KF supported on alumina andlanthanide imide and nitride on zeolite, and combinations thereof. 2.The process according to claim 1, wherein the amine is selected frommonoethanolamine (MEA), diglycolamine (DGA), diethanolamine (DEA),methyldiethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP), andpiperazine (PZ).
 3. The process according to claim 1, wherein the HPAsare selected from H₃PW₁₂O₄₀ and H₃PMo₁₂O₄₀.
 4. The process according toclaim 1, wherein the molecular sieves are selected from microporousaluminosilicates and zeolites.
 5. The process according to claim 4,wherein the zeolites are selected from HZSM-5, H—Y and H—X.
 6. Theprocess according to claim 1, wherein the mesoporous aluminosilicatesare selected from M41S aluminosilicates.
 7. The process according toclaim 6, wherein the M41S aluminosilicates are selected from MCM-41,SBA-15 and MCF.
 8. The process according to claim 1, wherein the claysare selected from AlCl₃/Al₂O₃, ZnCl₂/Acid treated clays, FeCl₃/graphite,SbF₅/graphite, AlCl₃/graphite, vanadium phosphates, aluminophosphates,CaO—ZrO₂, Sm₂O₃—ZrO₂, Yb₂O₃—ZrO₂, aluminum chlorofluoride (ACF) andaluminum bromofluoride (ABF).
 9. The process according to claim 8,wherein the ACF is AlCl_(x)F_(3-x), wherein x≈0.05-0.25 and the ABF isAlBr_(x)F_(3-x), wherein x≈0.05-0.25.
 10. The process according to claim1 wherein the heterogeneous proton donor acid catalyst is HZSM-5. 11.The process according to claim 1, wherein the heterogeneous alkalinecatalyst is MgCO₃.